Hydrorefining of crude oils



June 13, 1961 2,988,501

T. V. INWOOD HYDROREFINING OF CRUDE OILS Filed Aug. 18, 1958 2,983,501 pp HYDROREFINING F CRUDE OILS Texas V. Inwood, La Habra, Calif.,assignorjto Union Oil Company of California, Los Angeles, Calif., acorporation of California Filed Aug. 18, 1958, Ser. No. 755,579 15Claims. (Cl. 208-211) This invention relates to methods for thecatalytic hydrorefning of crude oils, particularly crude shale oils forthe elimination of organic sulfur, nitrogen, and oxygen compounds,gumand colorforming bodies, and the general upgrading thereof. Inparticular, the invention is concerned with methods for pretreating thefeed oil whereby upon subsequent preheating and contacting with thehydrorefining catalyst, the normally occurring deposition of solid orsemi-solid carbonaceous materials in the heater tubes, transfer lines,valves, and upper sections of the catalyst bed, is markedly reduced. IInbroad aspect, the invention consists in first mixing the raw feed oilwith a recycle portion of the refined liquid product, or a selectedfraction thereof, then allowing the mixture to settle by gravity orcentrifuging to facilitate the separation of a heavy asphaltic phase,and then heating the asphalt-lean raffinate oil mixture to hydrorefiningtemperatures and contacting it with the catalyst under hydrorefiningconditions. It is particularly preferred to recycle aportion of theproduct fraction boiling between aboutf350 'and 500 F., although anyother fractions ofthefeed may also be included. It has been found thatthis 'pretreatment materially reduces the deposition of gums, tars,coke, and other carbonaceous deposits, which constitutes Ia seriousproblem in the catalytic treatment of crude oilsat elevatedtemperatures.

The principal objective of the invention therefore is to provide methodsfor contacting crude oils with hydrorefining catalysts in such manner asto minimize the deposition of carbonaceous deposits upon the catalyst,and in the preheater tubes, transfer lines,`valves, etc. AnotherVobjective is to provide iiexible control means for reducing thepour-point of the final product to the desired degree. Still anotherobject is to 'provide means'for remov- 'ing the deposit-formingconstituents of crude oils, while maintaining maximum overall liquidyields. 'Another obiect is to avoid the added expense involved inseparating 'from crude oil feedstocks such conventional 'deasphalting'solvents as propane, butane, `light naphthas and the like. A specificobject is to prolong the total life of the hydrorefinng catalyst, and toprolong the life cyclebetweenregenerations thereof. Other 'objects willbe apparent from the "more detailed description which follows.

Feedstocks which may be treated hereini'nclude 'specifically crude shaleoil, reduced crudeshale oil, petroleum crude oils, or reduced crudes,residual fractions from the topping of such crude oils, or mixtures 'of'such materials. In addition mixtures of anyof the foregoing crude oilsor residual 'fractions may 4be treated lin admixture with distillatefractions. For example, mixtures of crude oils with naphtha fractions,light or heavy lgas 4oils andthe like, are also contemplated.

The process of this invention is especially adapted for the treatment ofcrude shale oils, yi.e. the full-range oil produced directly fromtheretorting of shale-rock. Crude :shale oils Apresent difiicult problemsin refining in that Ithey `contain a high proportion of asphaltenes andcarfboidsyand up to about 4% of `nitrogen in the form of forg'anicnitrogen' compounds. In addition, 'metals may be `present in the lformof Vporphyrin-metal complexes or other Aorgano-metallic compounds. Crudef shale 'oils also some- 'times possesan unusually high pour-point. Forexample, "the crude oil from Colorado shale -is'no'rmally fa Jgeliat il;n

Patented June 13, 1961 ice room temperature, and its .pour-point may bein excess of 100 F.

The crude shale oil described herein may be produced Vfor example by theretorting procedures described in U.S. Patents 2,501,153, 2,640,015, and2,640,019. In general, the retorting procedure consists in initiatingcombuston in a body of moving shale rock, and utilizing the hotcombustion gases to educt the oil from uncombusted shale rockupstreamwardly from the combustion zone.

From the standpoint of refining flexibility and economy, the mostdesirable initial treatment for such oils consists of catalytichydrorefining to decompose nitrogenous compounds and sulfur compounds,to hydrogenate asphaltenes and carboids, to decompose organo-metalliccompounds, and in general to improve the color and handleability of theoil for subsequent refining procedures such as cracking, reforming, andthe like. Such an initial treatment also increases the overall finalyield of refined products, while at the same time substantially reducingcorrosion problems throughout the subsequent refining treatment. Thefirst major difiiculty encountered in attempting to hydrorefine suchoils consists in the tendency of the oil to deposit carbonaceous solidsupon hot surfaces in the preheating or catalyst-contacting zones. Theexact nature of the deposit-forming constituents is not known, but theymay comprise any of lthe above-noted organo-metallic components,asphaltenes, carboids, and/ or ntirogenous compounds.

The foregoing problems may be partially or completely solved byconventional pretreatment steps such as vacuum distillation, thermalcoking, or liquid-phase deasphalting using lower parafns, but thesetreatments lead to other disadvantages. In all cases, the liquid yieldof final product is relatively low, e.g. between about -85%. Moreover,it will be apparent that all of these procedures involve an additionalstep requiring expensive equipment and substantial operational costs.The process of this invention, however, does not involve any unusualadded expense, and liquid yields in excess of 90% by volume areordinarily obtained.

In the treatment of crude shale oil another problem encountered is theviscosity of the oil, which inhibits its ability to fiow freely in apipeline. It is sometimes desirable, for reasons of economy, totransport the shale oil after a minimum of processing at the retortingsite, to a more distant refinery for final treatment. The mosteconomical form of transport is by pipeline, but this is practical onlyif the oil has a sufficiently low viscosity to flow freely during coldwinter months. It is, therefore, desirable to reduce the pour-point ofthe crude oil during the initial refining steps and thereby reduce itsviscosity, so that itmay be economically transported to amore favorablysituated refining site. This usually involves reducing the pour-pointfrom its initial -100 P. to about 2070 F.

A considerable degree of pour-point control is integrated into`theprocess of this invention. Thus, in the :preferred modification ofthe process, where `a portion of the heavy endsof the hydrorefinedproduct is recycled with the fesh feed, each pass throughthe reactorwill effect a further reduction in pour-point as a result of thehydrocracking of lhigh molecular weight paraflins inthe wax range. Itwould be undesirable'to attempt to effect .the desired pour-pointreduction by a single pass through `the"rea`ctor, inasmuch as this wouldentail the use of `'high temperatures leading to reduction in liquidyields, rapid coking kof the catalyst, etc. These disadvantages are"largely avoided where the heavy fraction of feed, or 5a -portionthereof, is recycled through the reactor; in effect, `the heavy ends ofthe feed are subjected to treatment lat 'a low'ernetspace velocity thanthe light fractions, `thus Yprovidingamore selective hydrocracking ofthe `heavier 3 molecules. To obtain maximum reduction in pour-point, therecycled portion of product should include a maximum proportion of theheavy ends, while if only minimum pour-point reduction is desired it ispreferable to recycle a lesser proportion of the heavy ends.

In the practice of this invention, it is feasible to recycle a portionof the full-range product, or a portion of the heavy ends thereof, or aportion of the mid-boiling-range materials boiling for example betweenabout S50-500 F. Generally, regardless of the boiling-range of thefraction recycle, it is preferred to recycle between about 0.1 and 5volumes thereof per volume of fresh feed. Best results are generallyobtained when the recycle rate is between about 0.2 and 2.5 volumes ofhydrogenated product per volume of fresh feed.

Though I do not wish to be limited by any theory as to the mechanisminvolved in the pretreatment process herein described, it is believedthat more than one' factor may be involved. The principal effect isobserved in a precipitation, or phase separation of heavier, moreviscous, asphalt-like material. This phase separation is not alwayssharp in the sense that a sharply defined interface is formed, but uponmixing the oils and allowing them to settle, a distinct qualitativeseparation of heavier materials is noted. The completeness and rapidityof the separation is materially improved by maintaining the mixed oilsat temperatures in excess of about 100 F., and preferably between about14C-250 F.

The asphaltic material which settles from the oil mixture may bewithdrawn by any conventional phase-separation technique, or if desireda sharper separation may be obtained by centrifuging. Where ordinarygravity settling is employed, it will normally not be possible to obtaina sharp separation of asphaltic materials by simple decantation, orwithdrawal of the lower phase, unless very extended settling periods areemployed. It is however an important feature of my invention that aquantitative phase separation is unnecessary, especially when using thepreferred product fraction for recycle. This preferred fraction'shouldinclude a substantial proportion of material in the 350-500" F. boilingrange.

This fraction includes a considerable proportion of partiallyhydrogenated, fused-ring aromatic hydrocarbons, e.g. tetralin and thelike. These compounds materially aid in preventing the subsequentprecipitation of coke, gums, and the like during preheating andhydrorefining, probably due to hydrogen transfer reactions. Thus, eventhrough the initial separation of asphaltic components is not complete,the remaining minor amounts may be tolerated in the preheating `andhydrodening equipment due to the presence of tetralin-likc hydrocarbonsin the recycled product, which effectively hydrogenate the cokeprecursors, thereby preventing the formation of gums, tars and coke.

The proportion of raw feed which is initially precipitated and removedas the asphalt-rich phase will usually comprise about 1-l0% by volumethereof. However, depending upon the amount and type of hydrogenatedproduct which is recycled quantities outside this range may sometimes beseparated. Also, where efficient separation is obtained, as e.g. with acentrifuge, the amount of asphalt-rich phase removed may sometimes bereduced to less than 1%. This asphalt-rich phase may be withdrawn andused in fuel oils, or it may be subjected to thermal coking,conventional solvent-deasphalting procedures or the like to recovertherefrom an addition quantity of asphalt-free oil for hydroreining.

In the hydrorefining step, the pretreated, mixed feed is contacted witha suitable sulfactive hydroreiining catalyst under conditions ofhydrorening. 'Ihe catalyst may be disposed in `a fixed stationary bed,or the various moving bed, or uidized bed techniques may be employed.Generally, the xed bed technique is most satisfactory. The catalyst maycomprise any of the oxides and/or suldes of the transitional metals, andespecially an oxide i M assessor or sulfide of a group VIII metal(particularly iron, cobalt or nickel) mixed with an oxide or sulde of agroup VIB metal (preferably molybdenum or tungsten). Such catalysts maybe employed in undiluted form, but preferably are distended andsupported on an adsorbent carrier in proportions ranging between about2% and 25% by-weight. Suitable carriers include in general the dicultlyreducible inorganic oxides, e.g. alumina, silica, zirconia, titania,clays such as bauxite, bentonite, etc. Preferably the carrier shoulddisplay little or no cracking activity, and hence highly acidic carriersare generally to be avoided. The preferred carrier is activated alumina,and especially activated alumina containing about 315% by weight ofcoprecipitated silica gel.

vThe preferred hydroreiining catalyst consists of cobalt oxide plusmolybdenum oxide supported on silica-stabilized alumina. Compositionscontaining between about 2%and$% of C00, 4% and 20% of M003, 3% and 15%,of .SiO2, and the balance A1203, and wherein the mole-ratio of COO/M003is between about 0.2 and 4, are specifically preferred. These catalystsare preferably prepared by alternate impregnation with yaqueoussolutionsjof `ammonium molybdate and cobalt nitrate, as described inU.S. Patent No. 2,687,381.

.Suitable hydrorening conditions are as follows:

Operative Preferred' 70D-850 A10G-3, 000 Y 1-10 50G-5, 000

Within the above operating conditions, the specific hydroreiiningconditions selected should be such as to meet required productspecifications.

The process of this invention will now be described in more detail inconnection with the attached flow sheet1 which is intended merely toillustrate the principal modiffications, .but is not intended to belimiting in scope'. The initial feedstock is brought in through line 1and preheated to the desired settling temperature in preheater 3, e.g.to about F. The preheated feed is then passed via line 5 into mixingvalve 7 wherein it is mixed with the recycled hydrorened product, orfrac'- tion thereof, from line 9. The mixture is then transferred vialine 11 to a settling tank 13, wherein the mixture is allowed tostratify, at e.g. 150 F., for a suflicient length of time to obtain thedesired separation. This time range is extremely variable, dependingupon the characteristics of raw feed, amount and type of productrecycle, and settling temperature, but ordinarily will range betweenabout 2 lhours and 48 hours. 'Ihe asphalt-n'ch phase is withdrawn vialine 15, and may be utilized for fuel oil via line 17. However, ifdesired, this material may be transferred via line 19 and preheater 21to thermal coker 23. The coking step generally involves heating theasphalt-rich oil to a cracking ternperature of e.g. 750950 F. and thenallowing it to soak in coker 23 for several minutes or hours whilecontinuously removing overhead the volatile products boiling in the gasoil range and below, and continuously precipitating coke on the walls ofthe coking vessel. Ordinarily, none of the liquid feed is removed asliquid, all being converted to coke, light gases, or distillates.

yEventually the coke which precipitates in coker Z3 will fill thevessel, and somewhat before this point is reached the operation must besuspended while the coke is removed. As the coke precepitates it adheresto the walls and becomes strongly agglomerated into a dense hard mass.This mass is ordinarily removed either by drilling out the drum, or bywashing it out with highpressure jets of water. While this operation isproceeding, ,the flow of oil in line 19 is diverted to another col;-

e.. n may.

The overhead product from coker 23 is transferred via v line 25 to line27, where vit `is mingled with the principal feed stream forhydrorelning as subsequently described.

The puritied oil in separator 13 is continuously or intermittenlywithdrawn via line 29 and passed via pump 3,1, line 27, preheater 33,and line 35 into the top of 'reactor 37, wherein hydrorening takes placeunder the conditions previously described. Recycle and makeup hydrogenfor the hydrorefining reaction may be blended with the feed, eitherthrough line 39 ahead of preheater 33, or it may be separately preheatedin heater 41 and admitted via line 43.

The total effluent from hydrorener 37 is withdrawn via line 45, cooledto e.g. ISO-250 F. in condenser 47 and transferred via line V49* tohigh-pressure separator (51.v Where crude shale oil is being treated, itis usually desirable to introduce a small amount of ywater or steam vialine 53, which is condensed in condenser 47 and elfects a scrubbing ofthe total product to remove therefrom soluble salts such as ammoniumchloride and ammonium sultides.

The waste wash water is withdrawn from separator 511 via line 55.Hydrogen-rich recycle gas is taken off via line 57, blended with makeuphydrogen from line 59, .and the mixture is then recycled via compressor61 into line 63 for use as previously described.

The liquid hydrocarbon product in separator -1 is withdrawn via line 65and flashed into low-pressure sepavrator vessel 67 from whichhydrogen-lean light gases containing methane, ethane, and the like, maybe withdrawn 'via line 69 and utilized as fuel gas or the like. Theiinal liquid product is withdrawn via line 71, and if a portion ,of thefull-range product is to be used for recycle, this portion is divertedthrough line 73` and recycled to mixing valve 7, via line 9. The netproduct in this case is recovered via lines 75'-, 83 and 81. If aselected fraction of the feed is to be used `for recycle, the entireliquid product is passed into line 75 and transferred in whole or inpart to distillation column 77 via line 79. Any portion of the liquidproduct which is not subjected to fractionation is passed directly intofinal product recovery line 81 Vvia line 83.

In fractionating column 77 a light overhead is ordinarily taken overheadand condensed in cooler 85- to mix with the final product in line 8.1.Where a full-range bottoms fraction is to be utilized for recycle, thetotal bottoms from column 77 is withdrawn via line 87, and is split intoa net product fraction in line 89 and a recycle portion passing tomixing valve 7 via lines 911, 93, and 9. This full-range bottomsfraction is preferably the 350 R+ fraction.

Where it is desired to utilize only a mid-boiling-range portion ofproduct for recycle, line 95 may be utilized to withdraw from one ormore trays of the column a fraction boiling e.g. between about 350 and500 F. Any selected cut within this range, or the entire range, may beutilized. This fraction may then be split into a net product fractiongoing to product recovery line 81 via line 97, and a recycle portionpassing to mixing valve 7 via lines 99, 93 and 9. In the event that onlythe side-cut is utilized for recycle, then the 500 F-ibottoms fractionremoved via line 87 is preferably passed entirely via line 89 to productrecovery line 811.

While it has been indicated that the overhead fraction boiling belowabout 350 F. is not recycled, it is not intended to preclude therecycling of part of this material along with either the heavy ends orthe side-cut fraction which is recycled. It will be apparent that manyother modications of the specific operations above `describedmay beemployed 'without departing from the eslimiting -in scope.

Example A crude shale oil educted from Colorado shale rock, said oilhaving a 50% boiling point of 680 F., a gravity of 20.4 API, containing1.84 Weight-percent nitrogen, and vhaving a Ramsbottom carbon residue of3 weightpercent, was subjected to conventional hydroreiining using acatalyst consisting of 3 weight-percent COO and 9 weightpercentMoO3,-impregnated on a carrier consisting of A1O3 and 5% coprecipitatedSiOZ. The conditions of hydroreiining were: pressure 3,000 p.s.i.g.,liquid hourly space velocity 2.0, hydrogen/oil ratio 6,000 s.c.f./bbl`.,and average temperature 735 F. After operating under these conditionsfor 35.5 hours, the pressure drop across the reactor had risen fromabout l inch of water to 27 inches, indicating that excessive pluggingof the reactor had occurred. The operation was hence discontinued and itwas found that the vcatalyst contained coke and gum deposits amountingto 0.06 weight-percent of the total feed processed. A portion of thesedepto-sits no doubt were initially formed in the preheater section ofthe reactor, and subsequently carried into the catalyst bed by theiiowing liquid feed.

*In another hydroreiining run, two parts of the crude shale oil and onepart vby volume of the 400 F.-}- bottoms from the hydrogenated productwere blended and allowed to settle for about 24 hours at 120 F. Aconsiderable precipitation of heavy asphaltic material was noted, whichprecipitation does not occur when the raw feed alone is allowed to standunder the same conditions. Upon drawing off the supernatant mixture ofraw crude oil and hydroreiined product, and subjecting the blend tohydrorening under the same conditions above described, it is found thatthe operation may be continued smoothly forA several weeks withoutexcessive pressure drop across the reactor,-and without significantdecline in catalyst activity. The final product is substantiallycompletely desulfurized and about 70% denitrogenated, -while thepour-point (of the product reconstituted with the 0-400" F. fraction ofthe initial product) is 2-10 F. lower than that of the total productobtained by -hydroreining the untreated crude oil.

It is hence apparent that by blending the relatively hydrogen-richproduct with the hydrogen-lean crude oil, and allowing the mixture tosettle, a rconsiderable and effective portion of the materials leadingto deposition of carbonaceous deposits causing plugging of the recatormay be removed, while at the same time the product has a lowerpour-point. This result may be obtained even though no more than 1-10%by volume of the raw feed is removed as the asphalt-rich phase.

The foregoing description of specific methods is not intended to belimiting in scope except where indicated. Many Variations will occur tothose skilled in the art, and all such variations which yieldessentially the same result are intended to be included. The true scopeof the invention is intended to be embraced by the following claims:

I claim:

l. In a process wherein a relatively hydrogen-lean crude oil feedstockis subjected to catalytic hydroretning at elevated temperatures withconsumption of hydrogen to produce a relatively hydrogen-lean renedliquid product, the improved method for reducing the deposition of solidcarbonaceous matter in the hydroreiining zone, which comprises blendingsaid feedstock with a recycled portion of said refined liquid product,said recycled portion boiling predominantly above about 350 F., thensubjecting the resulting blend to settling conditions at a temperaturein excess of 100 F. for a suicient length of time `to effect aliquid-liquid phase separation and separating (therefrom a minor, heavyasphalt-rich liquid phase and a major asphalt-lean liquid phase, heatingsaid asphalt-lean phase to a hydrorefining temperature, and subjectingthe heated oil to catalytic hydrorefining at a temperature between about600 and 900 F. in the presence of added hydrogen.

2. A process as defined in claim l wherein said recycled 'portion ofrefined product comprises about 0.2 to 2.5 volumes per volume of freshfeedstock.

3. A process as defined in claim l wherein said recycled portion ofrefined product is a portion o'f the heavy fraction thereof boilingentirely above about 350 F.

4. A process as defined in claim 1 wherein said recycled portion ofrefined product is a portion of the mid-boilingrange fraction. thereofboilingbetween about 350 and 500 F.

5. A process as defined in claim 1 wherein said recycled portion ofrefined product is a full-boiling-range portion thereof.

6. A process as defined in claim 1 wherein said feedstock is a crudeshale oil.

7. A process as defined invclaim 1 wherein the catalyst employed in saidhydrorefining zone is essentially a com- -posite of cobalt oxide plusmolybdenum oxide supported on a carrier which is essentially activatedalumina.

8. In a process wherein a relatively hydrogen-lean crude oil feedstockis subjected to catalytic' hydrorefining at elevated temperatures withconsumption of hydrogen lto produce a relatively hydrogen-lean refinedliquid product, the improved method forreducing the deposition of `solidcarbonaceous matter in the hydrorefining zone and vfor obtaining acontrolled reduction inpour-point of said liquid product, whichcomprises blending said feedstock with a recycled portion of saidrefined liquid product, said recycled portion of product including afull-range bottoms fraction thereof having an initial boiling point in.excess of about 350 F., then subjecting the resulting blend to settlingconditions at a temperature in excess of -l00 F. for a suicient lengthof time to effect a liquidliquid phase separation, and separatingtherefrom a minor heavy asphalt-rich liquid phase and a majorasphalt-lean liquid phase, heating said asphalt-lean phase to ahydrorelining temperature, and subjecting the heated oil to catalytichydrorefining at a temperature between about 600 and 900 F. in thepresence of added hydrogen and at superatmospheric pressures. v

9. A process as dened in claim 8 wherein said recycled portion ofrefined product comprises about 0.2 to 2.5

volumes per volume of fresh feedstock.

10. A process as defined in claim 8 wherein saidrercycled portion ofrefined product is a portion of the heavy fraction thereof boilingentirely above about 350 F.

ll. A process as defined in claim 8 wherein said recycled portion ofrefined product is a full-boiling-range portion thereof.

12. A process as defined in claim 8 wherein said feedstock is a crudeshale oil.

13. A process as defined in claim 8 wherein the catalyst employed insaid hydroreiining zone is essentially a composite of cobalt oxide plusmolybdenum oxide supported on a carrier which is essentially activatedalumina.

14. A process as defined in claim 8 including the steps of subjectingsaid asphalt-rich phase to thermal coking to produce coke and a cokerdistillate, and blending the resulting coker distillate with saidasphalt-lean phase for combined treatment in said hydrorening zone.

15. A method for converting a relatively hydrogen-lean crude shale oilto a refined product of reduced pourpoint suitable for use in theproduction of conventional petroleum-type products, which comprisesblending said shale oil with a relatively hydrogen-rich recycle productfraction produced as hereinafter defined, subjecting the resulting blendto settling conditions at a temperature -above about F. for a sufficientlength of time to effect a substantial stratication, separating from thesettling zone a minor asphalt-rich liquid phase and a major asphalt-leanliquid phase, heating said asphalt-lean phase to vhydrorefiningtemperature, and subjecting the heated oil to catalytic hydrorefining ata temperature between about 600 and 900, F. in the presence of addedhydro genY and at superatmospheric hydrogenating pressures, recovering acondensed liquid product from said hydrorefining, dividing saidcondensed liquid product into a net product portion and a recycleportion, subjecting said rccycle portion to fractional distillation torecover therefroman overhead fraction boiling below about 350 F. and abottoms fraction boiling above about 350 F., dividing said bottomsfraction intova net bottoms product portion and said recycle productfraction, and recycling said recycle product fraction to said initialblending step.

References Cited in the le of this patent UNITED STATES PATENTS2,606,141 Meyer Aug. s, 1942 FOREIGN PATENTS 362,458 Germany oct. 27,1922 430,438 Germany June 16, 1926 UMTIJD STATES PATENT OFFICECERTIFICATE 0F CORRECTION Patent N0'. 2,988,501 June 13, 1961 Texas V,Inwood It is hereby certified that error appears in the above numberedpetent requiring correction and that 'bhe said Letters Patent. shouldread as l-coI-Teoizec below.

Column 6, line 69, and column 7, line 3l, for "hydrogenlean", eachoccurrence, read hydrogen-rich Signed and sealed this 14th day ofNovember 1961.

(SEAL.)v

Attest:

ERNEST W.SWIDER DAVID L. LADD Attesting Officer Commissioner of PatentsUSCOMM-DC

1. IN A PROCESS WHEREIN A RELATIVELY HYDROGEN-LEAN CRUDE OIL FEEDSTOCKIS SUBJECTED TO CATALYTIC HYDROREFINING AT ELEVATED TEMPERATURES WITHCONSUMPTION OF HYDROGEN TO PRODUCE A RELATIVELY HYDROGEN-LEAN REFINEDLIQUID PRODUCT, THE IMPROVED METHOD FOR REDUCING THE DEPOSITION OF SOLIDCARBONACEOUS MATTER IN THE HYDROREFINING ZONE, WHICH COMPRISES BLENDINGSAID FEEDSTOCK WITH A RECYCLED PORTION OF SAID REFINED LIQUID PRODUCT,SAID RECYCLED PORTION BOILING PREDOMINANTLY ABOVE ABOUT 350*F., THENSUBJECTING THE RESULTING BLEND TO SETTLING CONDITIONS AT A TEMPERATUREIN EXCESS OF 100*F. FOR A SUFFICIENT LENGTH OF TIME TO EFFECT ALIQUID-LIQUID PHASE SEPARATION AND SEPARATING THEREFROM A MINOR, HEAVYASPHALT-RICH LIQUID PHASE AND A MAJOR ASPHALT-LEAN LIQUID PHASE, HEATINGSAID ASPHALT-LEAN